Such a camera module is configured as shown in FIGS. 7A and 7B.
As shown in FIG. 7A, a lens 1 for forming an image in an image pickup device (not shown) is held by the inner periphery of an inner lens barrel 2. The image has entered from the outside. A screwing part 3 is formed on the outer periphery of the inner lens barrel 2. The inner lens barrel 2 is screwed to and held by an outer lens barrel 5. The inner periphery of the outer lens barrel 5 has a screwing part 4 screwed to the screwing part 3 of the inner lens barrel 2.
In focus adjustment of the camera module, the protrusion amount of the inner lens barrel 2 is adjusted by rotating the inner lens barrel 2 relative to the outer lens barrel 5, and the inner lens barrel 2 and the outer lens barrel 5 are fixed to each other with a UV cured resin after the focus adjustment. Alternatively, as shown in the plan view of FIG. 7B, a laser beam 7 is emitted over a joint 6 of the screwing part 3 of the inner lens barrel 2 and the screwing part 4 of the outer lens barrel 5 to fix the inner lens barrel 2 and the outer lens barrel 5 by welding. Reference numeral 10 denotes a base part provided on the base end of the outer lens barrel 5. This welding technique is disclosed in the following non-patent document:
“Precision Micromachining of Home Information Appliances”, Naohisa Matsushita and Susumu Iida, Lecture Overview of FORUM on MICRO JOINING and PROCESSING 2004, pp. 34 to 38, published on Jul. 16, 2004 by “International Welding Show Forum Steering Committee” Secretariat, Sanpo Publications, Inc.
Generally, an LD laser device has a linear light-emitting part. When the laser beam 7 is passed through an optical fiber as described in the non-patent document, the light guide part (core) of the optical fiber is circular in cross section and thus the laser beam 7, which undergoes multiple reflection through the light guide part, is emitted in a circular spot with a diameter of about 0.2 mm. A part 8 of the inner lens barrel 2 and the outer lens barrel 5 is melted, solidified into a thin layer (depth: about 0.2 mm) as shown in FIG. 7C, and welded with a resin, so that focus is fixed. The rotational torque strength is about 0.6 to 1.4 N·cm. As shown in FIG. 7B, since the laser beam is emitted to only one point, an inner lens barrel 2 may be fixed while being displaced from the center by shrinkage during the solidification of the resin.
Techniques for laser-welding resin members are disclosed in many reports including Japanese Patent Laid-Open No. 60-214931. The following method is well known: a translucent resin allowing the passage of a laser beam and an absorbent resin absorbing a laser beam are stacked, and a laser beam is emitted from the side of the translucent resin to heat a surface of the absorbent resin, so that the resins are welded. Japanese Patent Laid-Open No. 62-142092 discloses a method of interposing an absorbent adhesive between resin members and heating the adhesive with a laser beam to join the resin members.
In fixation with a conventional UV adhesive, the curing time of the adhesive is long and thus tact time is increased. Further, since the adhesive is necessary, the manufacturing cost is increased. Moreover, it is troublesome to manage the adhesive.
In contrast to this technique, in the welding and fixing with the irradiation of the laser beam 7 in the non-patent document, it is possible to achieve short tact time and low manufacturing cost, and thus the technique of the non-patent document is suitable for mass production. However, with the irradiation of the laser beam in a circular spot having a diameter of about 0.2 mm, only the top surfaces of the inner lens barrel 2 and the outer lens barrel 5 are melted and cured, resulting in a low welding strength in relation to a large melted mark. Further, this technique causes undesirable appearance quality.
To be specific, when a melted resin portion caused by the irradiation of the laser beam is a thin surface layer, under use environment of high temperatures and humidity or in the event of an external torque and vibrations in the rotation direction, the melted resin portion may be easily destroyed and the position of the protruded inner lens barrel 2 may be changed. Thus, the focus position of the lens 1 may be changed and cause a defective image.
When laser irradiation energy and the spot diameter are reduced to form a smaller melted mark, welding strength further decreases. In the case of fixing by welding, the inner lens barrel 2 may be fixed while being displaced by shrinkage during the solidification of the resin.
An object of the present invention is to provide a manufacturing method of an optical component whereby fixing strength between the inner lens barrel 2 and the outer lens barrel 5 is improved, higher appearance quality is obtained, and fixing accuracy between the inner lens barrel 2 and the outer lens barrel 5 is increased.